The present invention relates to microelectromechanical systems. More particularly, the present invention relates to providing electrical connections in such systems. Microelectromechanical systems (MEMS) are small devices which provide certain electrical and mechanical functions and are typically batch fabricated. MEMS have found wide spread use in many electrical devices. Example MEMS include acceleration, pressure, flow, displacement, proximity, sensors and valves, pumps, and optical component actuators. One specific use for MEMS transducers is in pressure sensing applications.
In aviation or industrial fluid sensor applications, fluids (media) can corrode sensor elements, metal films and connections that are used in manufacturing the sensors. Corrosive process fluids can include gasses in an aerospace or stationary turbine engine, acids, caustics, oils, petrochemicals, foodstuffs and the like.
Sensor elements are preferably placed between layers of a sensor body and interconnects are also preferably between the layers and sealed so that corrosive process fluids do not come in contact with the sensor elements and interconnects.
In miniature devices that are made using MEMS (microelectromechanical systems) techniques, it is difficult to provide electrical interconnects between layers of the sensor body. This is true for sensors made with MEMS techniques. With MEMS bonding methods, the flat layers of the sensor body need to come together with precise alignment and extremely small gaps, without irregularities or protrusions between the layers. Interconnects that mechanically protrude will contact and hold the flat surface apart during bonding. Defective bonds or leaks can result.
Mechanical contact between interconnects needs to be avoided during bonding of the layers. Mechanical contact of the interconnects, is needed, however, in order to complete an electrical circuit at the interconnect. The two MEMS process needs conflict with one another.
An isolated connection is formed by growing interconnects from the grain growth of a electrically conductive grain growth material inside a MEMS device after the device is bonded together. The material used for grain growth of electrical contacts is deposited inside a cavity formed between first and second layers of the device. In one aspect, the material deposit is relatively flat at the time of assembly and does not interfere with bonding between peripheral edges of the cavity. After assembly of the first and second layers, the deposit is heated and grows an electrical interconnect forms through grain growth of conductive films or leads that are selectively deposited inside the cavity.